Abstract Although cancer cells are invariably shed into the colon during and after curative resection, their role in the colorectal cancer (CRC) recurrence following surgery remains unknown. Yet two facts remain: CRC recurrence remains unacceptably high and is increased in the setting of anastomotic leak, a problem occurring in upwards of 15% of patients. We identified that the local environmental context of major colon resection can shift a commensal microbiont (i.e. Enterococcus faecalis) into a high collagenase producing, MMP9 activating pathobiont that causes anastomotic leak. We recently discovered that collagenase producing E. faecalis can also interact with resident macrophages and shift cultured colon epithelial cells to express a mesenchymal-like phenotype with highly invasive and migratory behavior, displaying features of epithelial mesenchymal transition (EMT), a process involved in cancer metastasis. Taken together, it is plausible that shifts in the microbiome that develop following major colon surgery that allow collagenolytic strains such as E. faecalis to colonize anastomotic tissues, could link anastomotic leak to colon cancer when cancer cells are shed into the peri-anastomotic environment. In this proposal we hypothesize that following colorectal anastomotic surgery, exposure of anastomotic tissues to both collagenolytic pathobionts and colon cancer cells promotes the adherence to, and migration of CRC cells across the gut wall resulting in localized extramucosal tumor formation. We have developed a novel model of localized CRC in mice that involves exposure of mouse anastomoses to collagenolytic E. faecalis and dispersed CT26 colon cancer cells, such as might occur following surgery when the normal microbiome is depleted by antibiotics and the anastomosis is exposed to shed cancer cells. Through the lens of a highly representative surgical experimental model, we will therefore address three aims: (1) to define the community structure, membership, and function of the intestinal microbiome in a novel mouse model of colorectal anastomotic surgery that predicts localized tumor formation (2) to track and define the mechanisms by which CRC cells migrate across the gut wall to form localized tumors following their exposure to anastomotic sites in our mouse model (3) to demonstrate the critical and intersecting roles of normal microbiome maintenance in mitigating the processes by which CRC cells implant, migrate, and form localized tumors in our model. This work will open an exciting new area of surgical research and will provide excellent technical and scientific training for the applicant to help her develop into an academic surgeon and independent investigator.